The present invention relates to an improvement of a back of a water-resisting watchcase.
In recent years, there has been a demand for thinner watches. FIG. 1 shows an example of such thin water-resisting watches. A case body 1 has a square shape front and comprises a radially extending upper portion and an axially extending side wall portion. An annular recess 1a is provided in a bottom of the side wall portion for engaging an O-ring 2. A back 3 is secured to the case body 1 by a plurality of screws 4. A glass 5 is engaged with the radially extending upper portion of the case body 1 interposing a packing 6. A module 7 is disposed in the watchcase.
In this watchcase, the back 3 is made of stainless steel having longitudinal elasticity modulus of 18,000 kg/mm.sup.2. Explaining the deflection of the back having a rectangular shape, for example rectangle of 27.5 mm.times.23.5 mm, and having thickness a of 0.6 mm, if the watchcase is subjected to four atmosperic pressure, the back 3 is deflected 0.53-0.57 mm at a central portion thereof. In order to allow such a deflection, it is necessary to leave a space b between the back 3 and module 7 about 0.60 mm. Accordingly, if thickness c of the glass 5 is 0.6 mm, space d between the glass 5 and module 7 is 0.55 mm, and thickness e of the module 7 is 1.2 mm, the whole thickness t of the watchcase, that is, t=a+b+c+d+e, is 3.55 mm. Since a minimum thickness a of the back 3 and the minimum space b between the back 3 and module 7 are 0.6 mm respectively, it is difficult to decrease the thickness t less than 3.55 mm.